Field of the Invention
The invention relates to a device for the catalytic conversion of exhaust gases in an exhaust system, in particular in an exhaust system of a combustion engine, including a catalyst carrier body having a multiplicity of channels through which an exhaust gas can flow. The invention also relates to a process for manufacturing such a device.
In order to attain conversion of hydrocarbons and carbon monoxide contained in a combustion engine which is as complete as possible, the catalytic converter must be at a minimum temperature at which the catalytic conversion of components of the exhaust gas can take place. In general, that temperature is described as a so-called initiation temperature. The catalyst is heated during a cold starting phase by hot exhaust gas. It is also known to at least partially electrically heat the catalyst carrier body. In order to ensure that the output of pollutants is as low as possible during the cold starting phase, and for mechanical reasons, it has been proposed that the catalyst carrier body be constructed with an internal insulation in order to reduce heat loss to a housing and into the surroundings.
A device for catalytic conversion of exhaust gases in an exhaust system, in particular in an exhaust system of combustion engines, is known from German Published, Non-Prosecuted Patent Application DE 36 02 134 A1. That device is provided with a metallic catalyst carrier body disposed in a housing. The carrier body is provided with a large number of channels through which an exhaust gas can flow. The internal insulation of the catalyst carrier body is created according to German Published, Non-Prosecuted Patent Application DE 36 02 134 A1 in such a way that a radially inward facing collar is disposed in front of the catalyst carrier body. The height of the collar is 3-15% of the diameter of the catalytic converter, but at least 1 mm. A zone of eddy current is produced in the exhaust gas flow through the use of that collar and in that way direct contact of the hot exhaust gas with an outer annular region is avoided.
A device for the catalytic conversion of exhaust gases in an exhaust system is known from German Utility Model DE G 87 12 267.7 U1. The device includes a catalyst carrier body which is provided with a large number of flow channels for an exhaust gas and which is fitted into a sleeve-like housing. The housing is thermally insulated with respect to the catalyst carrier body. The insulation is obtained by placing the catalyst carrier body between end rings which close at least an outer layer of a metallic matrix body and thereby the outer flow channels in the matrix. In that way the outer region of the catalyst carrier body is provided with a closed air gap, through which exhaust gas does not flow and which serves as heat insulation.